Please checkout the vertical white nodes below my hot tub spillover shelf that look a little like icicles, they can be chipped off and the residue does bubble and fizz when place in several drops of 31% Muriatic acid. My guess would be calcium. Additionally the spillover shelf was recently redone in the last two years ( much to my dis-satisfaction, That's another story however). This is the only area that these stains/nodes appear, Could the materials used in the redo be contributing to this effect, or is this MY chemistry ? My test logs are available. Thanks, Pete.